21898991 has 4 divisors (see below), whose sum is σ = 22071552. Its totient is φ = 21726432.

The previous prime is 21898951. The next prime is 21898993. The reversal of 21898991 is 19989812.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21898991 - 2¹⁴ = 21882607 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21898993) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 86090 + ... + 86343.

It is an arithmetic number, because the mean of its divisors is an integer number (5517888).

Almost surely, 2^21898991 is an apocalyptic number.

21898991 is a deficient number, since it is larger than the sum of its proper divisors (172561).

21898991 is a wasteful number, since it uses less digits than its factorization.

21898991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 172560.

The product of its digits is 93312, while the sum is 47.

The square root of 21898991 is about 4679.6357764253. The cubic root of 21898991 is about 279.7744399426.

The spelling of 21898991 in words is "twenty-one million, eight hundred ninety-eight thousand, nine hundred ninety-one".